Indeed, this is pretty much exactly what the OP is talking about. The problem is that it's hard to bootstrap, since correct verification procedures are not widely-known.

TACK, what tptacek mentioned, is an orthogonal strategy for solving the same problem, but it assumes that some MITM will be detected. An ideal solution would involve a combination of both TACK and monkeysphere.

There's also convergence, which currently can work for the case where the client is undergoing MITM, but not the server. Add support for notaries to cache TACK responses and you are pretty secure.